Propellent charge comprising nitrocellulose

ABSTRACT

A dry compacted Caseless Propellant Charge comprising in addition to the usual constituents of a propellant explosive, a proportion of nitrocellulose having an average nitrogen content of 11.0 to 12.0 percent by weight.

Unite States Patent [191 Stevely et al.

[ Dec. 18, 1973 PROPELLENT CHARGE COMPRISING NITROCELLULOSE Inventors:Robert Reid Stevely, Saltcoats;

William Snodgrass Webster, Beith, both of Scotland Assignee: ImperialChemical Industries Limited, London, England Filed: Aug. 21, 1972 Appl.No.: 282,057

Foreign Application Priority Data Sept. 16, 1971 Great Britain 43,188/7111.5. CI 149/2, IOZ/DIG. 1, 102/101,

149/96, 149/97, 264/3 C Int. Cl. C061) 5/00, C061) 5/02 Field of SearchI. 102/DIG. l; 149/2,

Primary ExaminerLeland A. Sebastian Attorney-Cushman, Darby & Cushman [57] ABSTRACT A dry compacted Caseless Propellant Charge comprising inaddition to the usual constituents of a propellant explosive, aproportion of nitrocellulose having an average nitrogen content of l 1.0to 12.0 percent by weight.

6 Claims, N0 Drawings PROPELLENT CHARGE COMPRISING NHTROCELLULOSE Thisinvention relates to a propellant composition for caseless propellantexplosive charges, to charges made from such compositions and to amethod of making such charges.

The use of caseless propellant charges as the power source forprojectiles and for explosive percussion tools such as nail guns is nowestablished. However, the design of a satisfactory unitary propellantcharge having ballistic properties comparable to those of a granularcharge presents many problems and as yet caseless charges have notcaptured any significant proportion of the market. a

A caseless charge must be designed so that, on ignition, burning willnot be limited to the surface of the charge but will occur throughoutthe mass as in a loose charge. In one method of preparing caselesspropellant charges individual grains of propellant explosive compositionare compacted either dry or treated with plasticiser or solvent to stickthe grains together in a coherent mass. The degree of compaction isintended to be such as to bind the grains sufficiently to preventbreakage in normal handling but to leave the charge sufficiently friablethat the grains separate and burn as a loose charge on actuation of theprimer which is used to ignite the charge. It is extremely difficult toachieve a balance of the many factors involved so as to produce asatisfactory commercial charge which will burn reliably without leavinga residue which can jam breech mechanism of a nail gun.

It is an object of this invention to provide a nitrocellulose propellantcomposition which, in granular form, can be compacted to produce animproved unitary compacted caseless propellant charge.

We have found that propellant grains containing a proportion ofnitrocellulose having an average nitrogen content of 1 1.0 to 12.0% N byweight can be dry compacte d without solvent or adhesives to gi eirnproved unitary caseless propellant charges. The charges disintegratemore reliably under the action of the primer to simulate the ballisticeffect of a loose charge better than compacted charges hithertoavailable, and they can be handled in normal use without substantialloss due to breakage.

Accordingly, the propellant explosive composition of this inventioncomprises, in addition to the usual constituents of a nitrocellulosebased propellant explosive, a proportion of low nitrogen nitrocellulosehaving an average nitrogen content of 11.0 to 12.0 percent by weight.The propellant may conveniently be a singlebase propellant based on highnitrogen nitrocellulose having an average nitrogen content of 13.2 to13.4 percent by weight (guncotton), a double-base propellant containingnitroglycerine and guncotton nitrocellulose or a triple-base propellantcontaining nitroguanidine, nitroglycerine and guncotton nitrocellulose.

Preferably the proportion of low nitrogen nitrocellulose is within therange to 30 percent by weight of the total composition.

From a further aspect the invention includes a unitary caselesspropellant charge comprising compacted grains of the aforedescribedpropellant composition. The charge is conveniently cylindrical. Ifdesired for convenience, the charge may be formed with a surface indentto accommodate an appropriate quantity of a priming composition.

The invention also includes a method of making a unitary caselesspropellant charge which method comprises dry compacting grains of apropellant composition containing, in addition to the usual constituentsof a propellant explosive, a proportion of low nitrogen nitrocellulosehaving an average nitrogen content of l 1.0 to 12.0 percent by weight.Preferably the grains are compacted at a pressure within the range30,000 to 70,000 psi.

The propellant composition may be prepared in gran ular form inconventional manner, for example by incorporating into the composition asolvent or plasticiser for the nitrocellulose constitutents to form adough and shaping the dough into the required grain by moulding orextrusion as a cord which is subsequently divided. The grains mayadvantageously be porous. The porosity may be achieved in known mannerby initially including a removable filler in the composition which issubsequently removed from the grains. For example potassium nitratecrystals may be included and re moved by leaching out of the grains withwater. The amount of filler is preferably in the range 50 to 200 partsper parts by weight of the composition.

The invention is further illustrated by the following Examples in whichall parts and percentages are by weight.

EXAMPLE I 84 parts (as dry) of guncotton nitrocellulose having anaverage nitrogen content of 13.3% N vetted with 44 parts of ethylalcohol, 15 parts of low nitrogen nitrocellulose containing an averageof l 1.6 to l 1.8% N, 1 part of diphenylamine, 100 parts of potassiumnitrate and 66 parts of diethyl ether were mixed to form an extrudabledough. The dough was extruded through a die to form a cord 1.4 mmdiameter which was air dried and cut into disc-shaped grains ofapproximate thickness 0.32 mm. These grains were stepped in hot water(60C) to remove most of the potassium nitrate and air dried. They werethen tumbled in a pan with fine graphite (average particle size 100 y.)to give them a glaze coating to improve their free running propertiesand facilitate subsequent feeding to a mould. The composi tion of thegrains was Guncotton nitrocellulose 84 parts Low nitrogen nitrocellulose15 parts Diphcnylaminc 1 part Potassium Nitrate 1 part Graphite 0 4 part0.35 gram quantities of the grains were pressed in a mould at a pressureof 50,000 psi to form cylindrical pellet charges each having a diameterof 8.85 mm and a thickness of 3.8 mm with a circular primer indent inone of its flat faces of diameter 4.5 mm and 2.0 mm in depth.

The primer indent of each charge was filled with a priming compositionconsisting of 64 parts of lead styphnate and 36 parts of ground glassslurried in a solution of nitrocellulose. The slurry was dried andcovered with a thin protective coating of collodion.

The caseless propellant charge of this Example was tested in anexplosively actuated nail driving gun and it burned cleanly and hadballistic properties comparable to a corresponding loose granularcharge. It withstood normal rough handling without breakage.

EXAMPLE ll 74 parts (as dry) of guncotton nitrocellulose having anaverage nitrogen content of 13.3% N wetted with 40 parts of ethylalcohol, 25 parts of low nitrogen nitrocellulose containing an averageof l 1.8 to 12.0% N, 1 part of diphenylamine, 50 parts of potassiumnitrate and 60 parts of diethyl ether were mixed to form an extrudabledough. The dough was formed into grains which were steeped to remove thepotassium nitrate and glazed as described in Example I. The compositionof the resulting grains was Guncotton nitrocellulose 74 parts Lownitrogen nitrocellulose 25 parts Diphenylamine l part Potassium nitratel part Graphite 0.4 part 0.30 gram quantities of the grains were pressedin a mould at a pressure of 40,000 psi to form cylindrical unitarycharges of approximately the same shape and dimensions as the pressedcharges of Example I.

When the charges were primed as in Example I and tested in a nail gunthey burned cleanly with ballistic properties comparable to those of acorresponding loose charge. They withstood normal rough handling withoutbreakage.

EXAMPLE III 59 parts of guncotton nitrocellulose having an averagenitrogen content of 13.3 percent, parts of low nitrogen nitro-cellulose(average N content 11.5 percent) and 1 part of ethyl centralite wereslurried with 800 parts of water and 20 parts of nitroglycerine weremixed into the slurry to form a paste. The paste was dried in hot air,mixed with 36 parts of acetone and four parts water and 200 parts ofpotassium nitrate were added to form a dough which was extruded andgranulated as in Example I. The grains were steeped in hot water (60C)to remove the potassium nitrate and were subsequently air dried andglazed as described in Example I.

The composition of the grains was Guncotton nitrocellulose 59 parts Lownitrogen nitrocellulose 20 parts Nitroglycerine 20 parts Ethylcentralite 1 part Potassium nitrate 1 part Graphite 0.4 part.

0.25 gram quantities of the grains were pressed in a mould at a pressureof 30,000 psi to form cylindrical unitary charges of approximately thesame shape and dimensions as the pressed charges of Example I.

When the charges were primed as in Example I, and tested in a nail gunthey burned cleanly with ballistic properties comparable to those of acorresponding loose charge. They withstood normal rough handling withoutbreakage.

EXAMPLE IV 69 parts of guncotton nitrocellulose having an averagenitrogen content of 13.3 percent, 15 parts of low nitrogennitrocellulose containing an average of l 1.2 to 11.4% N, and 1 part ofethyl centralite were slurried with 800 parts of water and 15 parts ofnitroglycerine were mixed into the slurry to form a paste. The paste wasdried in hot air, mixed with 40 parts of acetone and 8 parts of waterand parts of potassium nitrate were added to form an extrudable dough.The dough was formed into grains which were steeped to remove thepotassium nitrate and glazed as described in Example I.

The composition of the grains was Guncotton nitrocellulose 69 parts Lownitrogen nitrocellulose 15 parts Nitroglycerine 15 parts Ethylcentralite 1 part Potassium nitrate 1 part Graphite 0.4 part 0.35 gramquantities of the grains were pressed in a mould at a pressure of 60,000psi to form cylindrical unitary charges of approximately the same shapeand dimensions as the pressed charges of Example I.

When the charges were primed as in Example I and tested in a nail gunthey burned cleanly with ballistic properties comparable to those of acorresponding loose charge. They withstood normal rough handling withoutbreakage.

What we claim is:

1. A unitary caseless propellant charge consisting of dry compactedgrains of a propellant composition comprising a high nitrogen contentnitrocellulose and 10 to 30 percent by weight ofa nitrocellulose of l 1to 12 percent nitrogen content by weight.

2. A propellant charge as claimed in claim 1 formed with a surfaceindent to accommodate an appropriate quantity of a priming composition.

3. A propellant charge as claimed in claim 2 wherein the surface indentcontains priming composition.

4. A propellant charge as claimed in claim 3 wherein the primingcomposition comprises lead styphnate.

5. A method of making a unitary caseless propellant charge which methodcomprises dry compacting grains of the composition of claim 1 atpressures in the range of 30,000 to 70,000 psi.

6. A method as claimed in claim 5 wherein the propellant grains areporous. 1

2. A propellant charge as claimed in claim 1 formed with a surfaceindent to accommodate an appropriate quantity of a priming composition.3. A propellant charge as claimed in claim 2 wherein the surface indentcontains priming composition.
 4. A propellant charge as claimed in claim3 wherein the priming composition comprises lead styphnate.
 5. A methodof making a unitary caseless propellant charge which method comprisesdry compacting grains of the composition of claim 1 at pressures in therange of 30,000 to 70,000 psi.
 6. A method as claimed in claim 5 whereinthe propellant grains are porous.